To strictly regulate the protein expression in a short period, it is necessary to regulate a process of protein translation from mRNA. This is because in case transcription from DNA to mRNA is regulated by inhibiting the transcription, the translation will not stop until mRNA is degraded.
There is a technique of stopping the translation of mRNA introduced into a cell, until the mRNA is irradiated with light having a predetermined wavelength (Non-Patent Literature 1). In this technique, a caged compound is bound in advance to mRNA to be injected, so that the caged compound prevents ribosome from moving on the mRNA. The caged compound is dissociated from the mRNA upon receipt of light having a predetermined wavelength. By utilizing this technique, it therefore is possible to initiate the translation of mRNA at a desired timing.